1. Field of the Invention
The present invention relates to an antenna arrangement employing a folded structure having first and second sections defining a transmission line and to a radio communications apparatus incorporating such an arrangement.
2. Description of the Related Art
Terminals for use in radio communication systems are increasingly becoming smaller and smaller, for example cellular phone handsets. Hence, there is a need to provide smaller antennas without sacrificing radiation performance or efficiency. A further requirement is to provide antennas capable of operating in a range of different radio systems, for example GSM (Global System for Mobile communications), UMTS (Universal Mobile Telecommunication System) and Bluetooth.
A range of compact antenna arrangements are known, for example helical and meander-line antennas, the latter as disclosed for example in International Patent Application WO 97/49141.
An object of the present invention is to provide an improved compact antenna.
According to a first aspect of the present invention there is provided a antenna arrangement comprising a folded structure having first and second sections defining a transmission line, wherein each of the first and second sections comprises a physically-shortened electric element having a respective feed point at its free end.
The first and second sections need not be exactly parallel, for example they could define a tapered transmission line. Similarly, the first and second sections need not be exactly symmetrical, but do need to take approximately the same route so that a transmission line is defined.
Such an arrangement enables the use of one feed point for each operational mode. Different operational modes may consist of transmit and receive functions, different systems (for example GSM and UMTS), different frequency bands, or any combination of these modes. By the use of a separate feed point for each mode, it is significantly easier to provide optimal loading and efficiency in all modes.
Top loading may be provided between the first and second sections, thereby improving antenna performance and providing a more uniform current distribution through the folded structure. Additional short circuit elements may be used to modify the impedance of the arrangement.
The relative impedance presented by the feeds may be altered by arranging for the conductors of the first and second sections to be of different width, or by arranging for one of the sections to comprise a plurality of conductors connected in parallel.
The antenna arrangement may include discrete components, particularly if it is fabricated on a substrate such as PCB or LTCC. Such components may vary the current distribution on the folded structure, or may implement a switching function.
Multi-band operation may be enabled by duplication of the folded structure, at a reduced scale, within the same volume.
According to a second aspect of the present invention there is provided a radio communications apparatus including an antenna arrangement made in accordance with the present invention.
The present invention is based upon the recognition, not present in the prior art, that by folding a meander-line or other physically-shortened electric antenna, improved performance can be provided in a reduced volume.